Abstract The hypothesis that human development and susceptibility to disease depend upon a complex interaction between inherited genes and environmental exposures has gained wide acceptance. In addition, theories linking in-utero exposures with adult-onset chronic disease causation are expanding. The explanation partially rests on epigenetic mechanisms that result in permanently altered gene expression after in-utero exposures. It has been recognized for years that environmental chemicals to which we are exposed may have an effect on hormonally related chronic diseases in humans. Organochlorines (HOCs), many of which have been banned for 30 years or more because of environmental health concerns, are present in the blood of most human beings alive today. HOCs resist degradation, bioaccumulate in fatty tissue, and are thus persistently present in the food chain. They have endocrine-disrupting properties at a variety of doses in many species, including humans. In laboratory animals, parental exposure to endocrine disrupters has been shown in multiple studies to affect the F1, and more recently, the F2, F3, and even F4 generations through transgenerational epigenetic mechanisms. In humans, however, studies of non-genomic inheritance of effects of parental exposure to environmental agents have rarely extended beyond the F1 generation. We propose to expand upon the original Michigan Fisheater studies and establish a multigenerational cohort (F0, F1, and F2 generations) consisting of the original parental participants, their sons and daughters, and their grandchildren. We have preliminary evidence that expression of a limited number of genes that control sex steroid metabolism are altered in F1 generation females, depending on estimated levels of in-utero exposure to maternal blood levels of PCBs and DDT. The proposed analysis will consist of age-appropriate telephone interviews to ascertain a medical history, an exposure history, and when applicable, a reproductive history for each participant. Gene expression of a representative number of genes controlling both the synthesis and breakdown of sex steroids, as well as pertinent steroid receptors, will be performed in the surviving parents and their sons, daughters, and grandchildren. Since exposure to organochlorines results in endocrine disruption, it follows that the examination of sex steroid gene expression after organochlorine exposure (F0 generation from direct exposure from fish meals and F1 generation from in-utero exposure) will more firmly establish their relationship and provide insights into the mechanisms involved. Sex steroid gene expression in the F2 generation will allow us to generate hypotheses concerning whether altered gene expression, if present, is due to transgenerational inheritance of epigenetic phenomena, inherited polymorphisms, or both, allowing us to explore in a future study whether transgenerational inheritance of epigenetic modifications resulting from endocrine disrupter exposure is possible in humans. Project Narrative We propose to study a multigerational cohort of fisheaters to study with the following objectives: 1) in the F0 generation, to examine the association between organochlorine exposure from fish meals and the gene expression of key genes involved in sex steroid metabolism; 2) in the F1 generation, to examine the association between in-utero exposure of maternal organochlorine levels (adjusting for the participant's own circulating levels) and the gene expression of key genes involved in sex steroid metabolism; and 3) in the F2 generation, to examine the gene expression of key genes involved in sex steroid metabolism, and to generate hypotheses concerning whether altered gene expression, if present, is due to transgenerational inheritance of epigenetic phenomena, inherited polymorphisms, or both. This will allow us to explore the possibility of the inheritance of transgenerational epigenetic modification in humans.